I can't take Miller in a big game yet against guys like Pryor and Smith. He has enormous potential and could do things here that neither Smith nor Pryor were able to do, but he hasn't done them yet. He has made a lot of progression though and seems to get the job done when needed (Wisky last year, last weekend on the scoring drive to get the 28-21 lead) and I have a feeling he will develop into a kind of playmaker who will be able to complete scoring drives when necessary in big games.
Now, on to Pryor and Smith.
Smith, as far as I'm concerned, was a very good passer and a guy who, if he had been a in a more aggressive system, could've easily thrown for 3500 yards by the time he was in his senior year. He was a capable runner, not nearly as dangerous as many QBs seen in the past decade, but he could certainly burn you for a first down. Honestly I think that after '05, far too much was made of him trying to be a pocket passer, and he lost a huge aspect of his game which had always been picking up 50 yards a game scrambles and forcing Ds to spy on him and worry about him. He still did that on occasion in '06, but to me, he was almost too worried about making sure people saw him as a pocket passer and nothing else.
He was always up for TSUN games and will always be remembered for those. Unfortunately he will also always be remembered for the Fiesta Bowl and his terrible performance in the biggest game of his career. Personally I think that game was an aberration, the result of poor decision making and overconfidence, but the tape and statistics are better evidence in these types of discussion.
Pryor was never the passer Smith was, but the difference wasn't so enormous that it ends the discussion. Pryor wasn't the runner Miller is now, but he was learning a bit I think, as evidenced by multiple 50 yard runs in '10 and some good scrambles against Iowa. He wasn't excellent in either the area of passing or rushing, but he had a good combination of each, and combined with being a freak athlete and big enough to avoid sacks, he was a very dangerous and very good player.
He never faced a good TSUN team, in fact he faced the weakest three teams they have had for many many years, but his MVP Rose Bowl and Sugar Bowl performances against good teams (better than ND '05) speak for themselves.
Overall I have to go with Pryor by a slim margin. His rushing ability is more stressing to a defense and his passing game was strong enough to force defenses to respect it. He was also able to come through with victories in the two biggest games of his career.